This invention relates generally to methods and apparatus for printing on two sides of a media sheet, and more particularly, to a media handling system which first feeds a media sheet with a first side exposed to a print source, then feeds the media sheet with a second side exposed to the print source.
Printing to two sides of a media sheet, referred to as duplex printing, is a desirable feature in printing systems, especially in desktop or office color printers as printing speeds increase. The advantages of duplex printing include reducing the amount of paper required compared to one-sided (simplex) printing, and generating print sets with layouts resembling that of professionally printed books. Conventional duplex printing devices employ complex paper handling mechanisms. Typically, an extra tray is used for temporary storage of pages having printing on a first side. In an alternative approach a second paper path is provided to route a first printed page around the existing paper supply. Another approach utilizes a media re-feed guide that positively blocks the movement of media along a first path of travel and directs the media travel along a second path.
Similarly, duplex copying typically is accomplished by either one of two methods. In one method, first side copies are stacked in a duplex tray. When a set of first side copies is complete, the copies are fed out of the duplex tray and returned with an odd number of inversions along a duplex path to receive second side imaging. In an alternative method first side copies are returned directly to receive second side imaging without stacking.
The development of new technologies to accomplish color office printing, such as solid or phase change ink printing has presented special problems to be overcome if successful duplex printing is to be achieved. Solid ink printing employs a wax-like ink base that is jetted at a molten temperature and then solidifies as it cools on intermediate and final receiving substrates. Printing on the second side of a media sheet without melting or destroying the hardened image on the first side has been a barrier to duplex printing. Paper curling has also been a problem.
Conventional devices to achieve duplex printing tend to have long paper paths, multiple imaging units, and many parts. It is desirable to achieve a simplified method and apparatus for duplex media handling at a desktop printer. These problems are solved in the design of the present invention.